Classification

Distribution

Endemic to the middle and lower Mekong River system in Laos, Thailand, Cambodia, and Vietnam. Its known range extends from Chiang Rai province, Thailand in the north to Kratie province, Cambodia in the south, and it occurs in several important tributary systems including the Sesan, Srepok, and Tonlé Sap.

Type locality is ‘Mekong River at Kemarat, Thailand’.

Habitat

Tends to inhabit medium to large-sized river channels and displays a preference for fast-flowing water, although it can be found in deeper, slow-moving stretches during the dry season. It is typically associated with rocky environments (see ‘Diet’) and adults tend to congregate in upland rivers with deep pools, rapids and inundated riparian forest.

Adults undertake seasonal migrations to forage in floodplains and breed in upstream areas while juveniles migrate downstream from headwaters to major rivers (see ‘Reproduction’), and dam construction throughout the Mekong basin is exerting a serious effect on the life cycle of this and many other migratory fish species. It is also highly prized commercially, fished intensively using gillnets, and surveys in recent years have revealed that stockNam Ous have declined considerably due to a combination of these factors.

Maximum Standard Length

Suitable only for public installations or the very largest, highly-specialised private aquaria.

Maintenance

A large, mature filter system, rigorous maintenance regime comprising weekly water changes of 50-70% tank volume, and provision of highly-oxygenated water with a degree of movement should be considered mandatory.

Water Conditions

Diet

Mekongina species are specialised grazers of periphyton, benthic algae, and other organisms which grow attached to submerged solid surfaces.

They are by no means herbivorous and should be offered meaty foods such as live or frozen chironomid larvae (bloodworm), Tubifex, Artemia, chopped prawn, etc., along with good quality, sinking dried products, at least some of which should contain a significant proportion of vegetable matter such as Spirulina or similar.

This species can be belligerent and aggressively territorial towards conspecifics and similarly-shaped fishes, especially when space is limited.

Sexual Dimorphism

Sexually mature females are likely to be deeper-bodied and may grow larger than males.

Reproduction

Breeds at the onset of the wet season in nature. Adults spawn in upland rivers and the juveniles migrate down to the main Mekong channel to forage, before migrating back upriver once sexually mature. It is during these movements that large numbers are fished both commercially and for subsistence.

M. erythrospila is occasionally in the ornamental trade but is unsuitable for the majority of private aquaria given its adult size.

It can be told apart from its only congener M. lancangensis by the following combination of characters: barbels absent (vs. a single pair of rostral barbels); four (vs. two) irregular rows of tubercles on the snout and head, with two enlarged tubercles on each side of the snout tip; 18-21 (vs. 19–27) rostral marginal lappets; 34-37 (vs. 38–41) lateral line
scales; 16 (vs. 18–20) circumpeduncular scales; 7-7½ (vs. 5½-6½) scale rows between the dorsal-fin origin and lateral line; snout longer, measuring 38.6-57.8% HL (vs. 31.9–36.9%); adpressed anal-fin shorter, not reaching (vs. reaching) the caudal-fin base.

Following the most recent update by Yang et al. (2008) the genus Mekongina can be distinguished from other cyprinids as follows: no spinous dorsal-fin ray; 10 branched dorsal-fin rays; rostral cap developed split into several papillate lappets; rostral cap not connected with lower lip; lower lip not modified into a mental disk; 0-1 pairs of barbels.

Mekongina is usually included in the subfamily Labeoninae/Cyprininae or tribe Labeonini (name varies with author) which by recent thinking is further divided into four subtribes; Labeoina, Garraina, Osteochilina, and Semilabeoina (Yang et al., 2012). The putatively monophyletic Semilabeoina comprises a number of genetic lineages including Placocheilus, Linichthys, Discogobio (including Discocheilus), Sinocrossocheilus, Pseudogyrinocheilus, Qianlabeo, Stenorynchoacrum, Rectoris, Hongshuia, Ptychidio, Parasinilabeo, Semilabeo, Cophecheilus, and Pseudocrossocheilus.

In addition, three species currently included in the polyphyletic genus Bangana fell within this group, as did two Garra species,The generic name Ageneiogarra Garman, 1912 has been suggested for the latter pair, although this does not appear to have been widely followed (e.g. Kottelat, 2013).

References

Fowler, H. W., 1937 - Proceedings of the Academy of Natural Sciences of Philadelphia v. 89: 125-264Zoological results of the third De Schauensee Siamese Expedition. Part VIII - Fishes obtained in 1936.

Kottelat, M., 2013 - Raffles Bulletin of Zoology 27: 1-663The fishes of the inland waters of southeast Asia: a catalogue and core bibiography of the fishes known to occur in freshwaters, mangroves and estuaries.